Philosophers as well as jurists distinguish between questions de facto and de jure, i.e. questions of factualness and questions of right. For example, for Smith to be guilty of murdering Jones, he must be shown to have done so both de facto (Smith did in fact kill Jones) and de jure (Smith killed Jones without legal justification).
With respect to theism vs atheism, the de facto question is: Does God exist?
In recent years, it has become fashionable for atheist apologists to completely evade answering the de facto question, much less to make a case the negative answer. Instead, they proclaim that “atheism is merely a lack of belief in the existence of God” and insist that such a lack of belief is different from a positive belief that God does not exist. This is a faulty and dishonest definition of atheism as I and others have explained elsewhere, but that is not the present point. The present point is this:
Atheists cannot evade the de facto question of whether God exists by switching grounds to de jure questions about whether belief in God is warranted, rational, epistemically justified, etc.
The reason, in a nutshell, is that what is warranted or rational or epistemically justified to believe depends at least in part on the answer to the de facto question. More specifically, if man has been created by God in the image of God in such a way that we in part resemble God in having higher cognitive powers and such that it is our end and greatest good to know God, then it is overwhelmingly probable that the human cognitive powers which produce belief in God are working properly when they produce a belief in God. It is only on the assumption that there is no such entity as God that it becomes at all likely that our cognitive powers are malfunctioning when they produce a belief in God. In other words, the very nature of epistemic warrant will be different in a case where God exists and one where God does not exist. If God does exist, then it is overwhelmingly probable that our cognitive powers are malfunctioning when they produce a belief that God does not exist or when they produce a belief that there is insufficient warrant for to believe that God exists. In brief, if there is a God, then atheism is almost certainly some sort of cognitive malfunction or dyscognition.
This argument is put forward by Alvin Plantinga in his Knowledge and Christian Belief. It is not my argument, but it is, as far as I can tell, decisive. I have sometimes been accused of being unoriginal in argumentation, but this seems to miss the point made by Socrates: it is rational to follow the strongest λόγος (argument) regardless of its source. Truth is much more important than originality, and I think every theist and every atheist should understand this point. So I am going to quote Plantinga at some length:
The De Jure Question Is Not Independent of the De Facto Question
And here we see the metaphysical or ultimately religious roots of the question concerning the rationality or warrant or lack thereof for belief in God. What you properly take to be rational or warranted depends upon what sort of metaphysical and religious stance you adopt. It depends upon what kind of beings you think human beings are, what sorts of beliefs you think their faculties will produce when they are functioning properly, and which of their faculties or cognitive mechanisms are aimed at the truth. Your view as to what sort of creature a human being is will determine or at any rate heavily influence your views as to whether theistic belief is warranted or not warranted, rational or irrational for human beings. And so the dispute as to whether theistic belief is rational (warranted) can’t be settled just by attending to epistemological considerations; it is at bottom not merely an epistemological dispute, but a metaphysical or theological dispute.
You may think humankind is created by God in the image of God — and created both with a natural tendency to see God’s hand in the world about us, and with a natural tendency to recognize that we have indeed been created and are beholden to our creator, owing him worship and allegiance. Then, of course, you will not think of belief in God as a manifestation of any kind of intellectual defect. Nor will you think it is a manifestation of a belief-producing power or mechanism that is not aimed at the truth. It is instead a cognitive mechanism whereby we are put in touch with part of reality — indeed by far the most important part of reality. It is in this regard like a deliverance of sense perception, or memory, or reason.
On the other hand, you may think we human beings are the product of blind evolutionary forces; you may think there is no God, and that we are part of a Godless universe. Then you will be inclined to accept the sort of view according to which belief in God is an illusion of some sort, properly traced to wishful thinking or some other cognitive mechanism not aimed at the truth (Freud) or to a sort of disease or dysfunction on the part of the individual or society (Marx).
This dependence of the question of warrant or rationality on the truth or falsehood of theism leads to a very interesting conclusion. If the warrant enjoyed by belief in God is related in this way to the truth of that belief, then the question whether theistic belief has warrant is not after all independent of the question whether theistic belief is true. So the de jure question we have finally found is not, after all, really independent of the de facto question; to answer the former we must answer the latter.
This is important: what it shows is that a successful atheological objection (i.e., an objection to theistic belief) will have to be to the truth of theism, not merely to its rationality, or justification, or intellectual respectability, or rational justification, or whatever. The atheologian who wishes to attack theistic belief will have to restrict herself to objections like the argument from evil, or the claim that theism is incoherent, or the idea that in some other way there is strong evidence against theistic belief. She can’t any longer adopt the following stance: “Well, I certainly don’t know whether theistic belief is true — who could know a thing like that? — but I do know this: it is irrational, or unjustified, or not rationally justified, or contrary to reason or intellectually irresponsible or. . . .” There isn’t a sensible de jure question or criticism that is independent of the de facto question.
This fact by itself invalidates an enormous amount of recent and contemporary atheology; for much of that atheology is devoted to de jure complaints that are allegedly independent of the de facto question. If my argument so far is right, though, there aren’t any sensible complaints of that sort.
Plantinga, Alvin. Knowledge and Christian Belief (pp. 40-41). Wm. B. Eerdmans Publishing Co.. Kindle Edition.
I encourage the interested reader to read the entirety of Chapter 3 of Plantinga’s book, or even—God forbid—the whole book.
Plantinga’s basic point seems both true and obvious to me. There cannot be a “neutral” epistemological standpoint because any discussion of the nature of belief and of warrant will involve a philosophical anthropology, that is, a doctrine of what human beings are and what cognitive power they possess. And any philosophical anthropology is the same as or a part of a metaphysics of man, which in turn will be a part of an overall metaphysics or general ontology. And a theistic metaphysics will necessarily look very different from an atheistic metaphysics. To use imagery from Plato, a theistic metaphysics will always hold that the readily observable reality around us, although real, is limited, as in the inside of a cave; and that there is much more to reality than is readily apparent, but that the higher portions of reality can become evident to one who learns how to see properly. An atheistic metaphysics, on the other hand, will hold a priori that the cave is exhaustive of reality; that there is not anything like a higher reality, and a fortiori no cognition of any higher reality.
So when an atheist attacks a theist on de jure epistemological grounds (e.g. by claiming “there is no evidence that God exists”), he is actually committing a petitio principii—that is, he is begging the question—he is assuming the truth of an atheistic metaphysics and its attendant epistemological consequences while pretending it is an epistemologically neutral position.
But there is no such neutral ground. If God does exist, then all or almost all those who have formed the belief that God exists have done so with warrant, and those who have formed the belief that no God exists or the belief that belief in God has insufficient warrant are the ones whose cognitive powers are dysfunctional or malfunctioning.
Atheism, then, whether it is construed as a belief that God does not exist or as a belief that belief in God has insufficient rational warrant, would then be a kind of cognitive malfunction or dyscognition, as I have said elsewhere. It is the atheist, not the theist, who is displaying a very deep kind of irrationality.
At the very least, the burden falls on the atheist to demonstrate that God does not exist before it is rational to accept any account of human cognition in which belief in God is deemed to be irrational or unwarranted. Until the atheist does so, the theist is perfectly within her epistemic rights to dismiss atheistical epistemic objections as merely question-beggingly assuming an atheistic ontology.